Clutch assemblies have been used for many years for engaging a vehicular transmission with an engine crankshaft to provide selected transmission gear ratios at preselected speed ranges for effective movement of the vehicle particularly under load.
One of the problems, however, particularly in heavy duty truck applications, has been regulating the rate at which the engagement occurs i.e. abruptly or in a smooth controlled manner of which the former is highly undesirable due to impact shock and undue damage and wear on the clutch plate as well as other parts of the transmission and drive train.
In view of the foregoing, considerable attention has been given in the past to controlling the rate at which the clutch plate engages the engine crankshaft so as to minimize shock load, damage and wear.
One of the ways utilized in the past for controlling the rate of engagement has been to control the actuator (characteristically a linear actuator) that actually effects the engagement with a control signal that progressively diminishes as the actual engine speed approaches a desired engine speed so as to progressively decrease the rate of movement of the clutch plate as it moves towards the engine crankshaft driver plate. This type of control, however, is not entirely satisfactory for it does not compensate for how fast the actual engine speed approaches a desired engine speed.
An early example of a hydraulic transmission control device for controlling the rate of engagement according to correlation between the engine speed and throttle position further including means for detecting variations in the rate of change in engine speed from a predetermined desired rate is disclosed in U.S. Pat. No. 3,004,447, the disclosure of which is incorporated herein by reference.
An example of an electronic clutch control which utilizes differences between clutch output speed and input speed in addition to acceleration of input speed to control rate of clutch engagement is disclosed in U.S. Pat. No. 3,752,284, the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 4,081,065, the disclosure of which is incorporated herein by reference, discloses an electrically controlled power clutch that is operative to control the rate of engagement according to an error signal "E" received by the actuator where ##EQU6## where N=actual engine speed
The desired engine speed is varied with the throttle pedal position so if the operator applies full throttle indicating a need for maximum starting torque, the desired engine speed is set near the peak torque of the engine. A light throttle position indicates a desire for slow maneuvering speed so the desired engine speed is set low. However, this control is deficient since it does not include the time rate of change of the desired engine speed to modify the clutch engagement.
An example of electrical clutch control systems that utilize an engine speed signal and two reference signals for controlling clutch engagement is respectively disclosed in U.S. Pat. Nos. 4,413,714 and 4,432,445, the disclosures of both of which are incorporated herein by reference.
All of the above however use either the error signal corresponding to the difference between actual engine speed and desired engine speed singularly or in conjunction with an acceleration term concerning acceleration of the engine or clutch plate and/or two or more additional reference signals for providing their clutch engagement rate control systems with the latter requiring the cost and expense of requiring additional sensors to provide the required information which, in itself, leads to higher probability of inaccuracies due to non-linearity or other quality problems associated with sensors in general.
Suitable vehicle starting depends upon the value of a number of factors and their time rate of change. By letting these factors modify the desired engine speed and including the influence of their time rate of change by including the time rate of change of the difference between the desired engine speed and actual engine speed a simpler improved clutch engagement control is attained.